The term powdered detergent has more than one meaning. In the most basic sense a detergent is the surfactant used for washing clothes, typically as a soda ash/surfactant/silicate agglomerate collection. In the home laundry market a detergent is a formulation used for washing clothes; as such, a detergent includes the soda ash/surfactant/silicate combination, and may also include granules of opacifiers, perfumes, and other ingredients. Here the term detergent is limited to the sense of a soda ash/surfactant/silicate agglomerate collection, unless otherwise noted.
A detergent is sometimes characterized by its loose bulk density, which is the weight per unit volume of detergent, determined without tapping. In the home laundry market, the formulation sold to the consumer preferably has a loose bulk density of from 600 g/L to 800 g/L. The soda ash/surfactant/silicate agglomerate that is used in such home laundry formulations is typically prepared using either a densifying spray tower, or a high shear mixing device followed by a fluid bed dryer. Both methods are capital intensive to install, and expensive to operate. Other more economical processes have not provided a suitable soda ash/surfactant/silicate aggregate. Such other processes include the typical high-bulk-density agglomeration methods, which generally are limited to producing a soda ash/surfactant/silicate powder aggregate that is used in home laundry formulations having a loose bulk density of 801-961 g/L (50-60 lb/cu ft) and the traditional spray drying methods, which are generally limited to producing a soda ash/surfactant/silicate aggregate that is used in home laundry detergent formulations having a loose bulk density of 320-480 g/L (20-30 lb/cu ft). Because of competitive pressures, the use of less expensive equipment, both in initial cost and also an on-going operating expense basis, is desirable.
U.S. Pat. No. 4,992,079 assigned to FMC Corporation teaches one such useful process.